1. Field of the Invention
The present invention relates to molded wooden products, and more precisely, to wooden products formed by molding wood fibers under compression.
2. Description of the Related Art
In general, molded wooden products are manufactured by molding wood fibers, obtained by chopping or shaving wood, under compression and utilizing the binding properties of the wood fibers to form the products. These molded wooden products are so-called hard boards and are substantially uniform in composition, light in weight, and possess few defects. They have been widely utilized, for example, as interior materials for constructing furniture, interior substrates for cars, and materials for television and stereo cabinets. The surface of the products is smooth and has good heat- and moisture-resistance properties. Moreover, the products are relatively strong in relation to their overall thickness.
Molded wooden products are typically manufactured by a wet shaping method in which wood chips are treated to form wood fibers. A synthetic resin and cellulose paper are incorporated into the wood fibers and the mixture is dispersed in water. The mixture is then filtrated under pressure and pressed under vacuum (for so-called mat-making). The mat (soft fiber plate) thus obtained is then shaped under hot compression.
A mat B obtained by the above described method is shown in FIG. 16. The mat B is shaped by a shaping mold 11 comprising an upper mold 13 and a lower mold 12 as shown in FIG. 17. The upper and lower molds are heated by hot plates 14, as shown in FIG. 17. In the drawings, M represents a molded wooden product, and M' represents excess materials which remain after the mat has been shaped.
Conventional molded wooden products are manufactured by the above-mentioned hot-press shaping method in which a mat comprised of wood fibers is pressed and shaped under heat. In order to increase the strength and rigidity of the molded wooden products, a plurality of mats are pressed together and the thickness of the final product is thereby increased. Accordingly, an excessive amount of raw materials are required, and the resultant product is unnecessarily heavy.
The prior art attempted to eliminate these drawbacks by selectively stacking mats at only those parts of the mold corresponding to the portion of the molded wooden product which requires increased strength and rigidity. For example, mats may be stacked around the periphery of the mold so that only the peripheral portions of the molded product are thicker. However, it is difficult to make the part of the mold for shaping the thicker portion of the product completely identical to the shape of the piled mats in the cavity of the mold, and therefore, the portion between the thickened part and immediately adjacent parts in the molded product does not have the same density as the thickened portion. This variation in density causes the strength of the adjacent portion to be less than that of the thickened portion.